Sound-reproducer.



PATENTED JULY 11, 1905.

' T. H. MACDONALD. SOUND-REPRODUGBR.

APPLICATION FILED APE. 17.1903.

511 vzwtoz wan zone UNITED STATES Patented July 11, 1905.

PATENT OFFICE.

THOMAS' H. MACDONALD, OF BRIDGEPORT, CONNECTICUT, ASSIGNOR TO AMERICAN GRAPHOPHONE COMPANY, OF WASHINGTON, DISTRICT OF COLUMBIA, A CORPORATION OF WEST VIRGINIA.

SOUND-REPRODUCER.

SPECIFICATION forming part of Letters Patent No. 794,416, dated July 11, 1905.

Application filed April 1'7, 1903, Serial No. 153,143. I

- To all whom it may concern.-

Be it known that I, THOMAS H. MACDONALD, a resident of Bridgeport, Connecticut, have invented a new and useful Improvement in 5 Sound-Reproducers, which invention is fully set forth in the following specification.

This invention relates to the construction of sound-reproducers for use with sound-records of the laterally-undulating type. In

such reproducers the stylus and its carryingbar constitute a lever of the first-class fulcrumed to the diaphragm box or casing. The improved reproducer may, however, be used with sound-rec0rds of the vertically-undulating type. Itis important thatthe stylus-bar be I attached to the casing by a rigid connection, loose joints, which give rise to rattling noises in operation, being avoided. To this end the stylus-arm has usually been attached to the casing by means of a flat spring or springs,

which make a rigid connection, while permitting the limited vibration of the stylusbar. In some cases the stylus-bar has been mounted to rock on a knife-edge or on cen- 2 5 t ers, being held firmly thereon by springpressure exerted on one or on both sides of the axis of oscillation at points relatively remote to said axis. In all such constructions it is manifest that the stylus-bar in vibrating has not only to actuate the diaphragm, but has to overcome spring-pressure in its movement in one or both directions. Study of the operation of such instruments shows that they cause undue wear upon the records and that while giving good and full reproductions of loud fundamental tones do not render well the finer shades of sound represented by the overtones. The explanation is that the overtones which give quality or tone color to the 4 sounds are represented in the sound-record by i very minute irregularities or undulations. A stylus drawn with considerable power and speed along these undulations must be able to vibrate with minimum resistance and friction in order to respond to them. The resistance of the stiff spring or springs above referred to prevents such responsiveness, and hence these finer irregularities are inadequately reproduced and with relatively little wear are obliterated.

The present invention consists in a stylusmounting which secures the requisite rigidity with minimum friction and resistance. To this end the stylus-bar (or a rock-bar to which it is rigidly attached) is supported on steel centers brought to a fine point, so that friction is practically eliminated, which centers are held to their bearings by pressure exerted in the plane of the axes of the centers, offering very slight resistance to the vibration of the stylus-bar and diaphragm in either direction. This pressure may be obtained by a spiral spring or springs in the plane of the centers. A spring of this kind while giving all the pressure desired in the line of its axis is free to oscillate laterally, and hence offers little, if any, resistance to the rocking of the lever. In lieu of spiral springs rubber tubing or cushions may be used; but metal springs are preferred. This pressure can be made as great as necessary to insure that the bar is not unseated. This construction is radically different from that wherein the stylus-bar rocks upon a knife-edge or centers in a plane parallel to that of the stylus-bar and is held on itsbearings by spring-pressure. In such case the vibration causes a side movement upon the knife-edge, to oppose which a heavy spring-pressure is necessary, and this springpressure opposes the vibration of the diaphragm, to a greater or less, extent obliterating the overtones. Furthermore, the spring (if one be used) has a tendency after the lever is thrown ofi its center to carry it still farther off, so that generally two springs are used, one working in opposition to the other.

In the present invention the lever-arm is simply fulcrumed on the centers (or knifeedge) on one side and on spiral springs on the other, the axes of the centers being at right angles with (instead of parallel to) the stylus-arm.

This construction serves, further, to keep the diaphragm perfectly neutral, there being no stress in either direction.

In the accompanying drawings, Figure 1 is an elevation looking toward the diaphragm of a reproducer constructed in accordance with the invention. Fig. .2 is a cross-section on line :22 00, Fig. 1; and Fig. 3 is a side view.

1 represents the diaphragm-casing, 2 the sound-conveying tube, and 3 the diaphragm. The stylus bar or lever 4 is attached at one end to the diaphragm in any suitable way. At the other end it is rigidly attached to a projection 5 of rock-bar 6.

7 is the continuation of the stylus-bar, having the usual socket to receive the stylus and the set-screw 8 to hold it in place.

Parts 4, 5, 6, and 7 constitute one solid piece. Rock-bar 6 is balanced on pointed centers 9 on a block 10, which is an extension of the diaphragm-casing, bar 6 being provided with conical seats 11, Fig. 2. The seats 11 have a greater angle than centers 9, the latter being, say, sixty degrees and the former forty-five degrees. Block 10 is also drilled to receive two screws 12, which pass loosely through holes in bar 6-, the axes of the screws 12' and of the centers 9 being all in the same plane and being at right angles to the stylus-bar 4. Between the heads of screws, pins, or post 12 and bar 6 are compressed coiled springs 13, which press the bar firmly upon its centers. Owing to the form and location of these springs, the pressure necessary for this purpose is secured without putting any stress on the diaphragm or materially opposing its vibration. Where the spring is attached at one side of the line of oscillation, the above-mentioned disadvantages result, and, moreover, the stylus-bar has a tendency to pivot where the spring is attached and unseat itself from its fulcrum, causing a side movement thereon and gradually loosening and wearing the hearing. In the construction herein shown the tendency ot the spring-pressure is always to set the centers more firmly in their seats. The construction is that of a lever fulcrumed on one side upon the centers and on the other side upon coil-springs.

It will be seen from Fig. 2 that the points of centers 9 and the bearings of springs 13 are all in the same line and that this line, which is the axis of oscillation of the stylusbar, also intersects the axis of the extension 7 of the stylus-bar. It will also be seen that this line of oscillation is in the plane of the diaphragm: 3, so that in normal conditions the neutrality of the latter is preserved and it is in the best condition to respond to the vibrations transmitted from the record. It will further be seen that the axes of the centers 9, springs 13, and screws 12 are all in the same plane, (represented by line a at, 1,) which plane passes through the axis of oscillation of the bar and is transverse to the plane (represented by line 525, Fig. 1) in which the stylus-bar oscillates. The springs therefore exert pressure in said plane to tension the centers. In the particular embodiment shown in the drawings said plane, as well as the axis of oscillation of the stylus-bar, are both transverse to the axis of the stylus.

There is in the entire mounting a very slight resistance other than the inertia of the diaphragm to oppose the small vibrations representing the overtoncs, the absence of which renders the reproduction thin and unmusical.

The advantages of the construction maybe in great part realized by substituting a knifeedge for the centers, and other modifications may be made without departing from the spirit of the invention.

What is claimed is- 1. In a sound reproducer, a stylus bar mounted to oscillate on an axis transverse to the axis of the stylus, and means for exerting pressure in a plane of said axis of oscillation transverse to said stylus to tension said hearing of said bar.

2. In a sound-rcproducer, a stylus bar or lever fulcrumed on centers and means for exerting pressure to tension said centers, said pressure being exerted in the plane of the axes of the centers, and the plane of the axes of said centers being transverse to the plane of oscillation of said bar;

3. In a sound reproducer, a stylus bar mounted to oscillate on: an antifriction-b earing, means for exerting spring-pressure in a plane of the axis of oscillation of said bar to tension said bearing, said: plane being transverse to the axis of the stylus.

a. In a sou nd-reproducer, the combination with the diaphragm, of a stylus-bar mounted to oscillate upon an antifriction-bearing, a coiled compression-spring for holding the bar on said bearing, the axis of said coiled spring being substantially in a plane of the axis of oscillation of said bar transverse to the bar atthe bearing.

5'. In a sound-reproducer, the combination with the diaphragm, o f a stylus-bar mounted to oscillate upon centers, and a coiled compression-spring for holding said bar on its centers, the axis of said spring being substantially in the plane of themes of said centers, and a pin or post encircled by the spring, said pin or post having a heador projection against which one end of thespring bears in holding the bar on its centers and the axis of said pin or post being substantially in said plane of the axes of the centers.

6. In a sound-reproducer, a stylus bar or lever fulcrum'ed on centers and held thereon by spring-pressure exerted in theplane of the axes of the centers, which plane is transverse to the axis of the stylus.

7 In a soundreproducer, a stylus bar mounted tooscillate on an antitriction-bearing and held thereon by spring-pressure exerted in the plane of the axis of oscillation, said plane being transverse to the axis of the stylus.

8. In a sound reproducer, a stylus bar mounted to oscillate upon an antifriction-bearing, and held thereon by coiled compressionsprings whose axes are in the plane of said bearing.

9. In a sound-reproducer, the combination with the diaphragm,- of a stylus-bar fulcrumed upon centers at right angles to the axis of the stylus, and held upon said centers by springpressure exerted in the plane thereof.

10. In a sonnd-reproducer, the combination of a-stylus-bar rigidly connected to a rock-bar having conical seats, pointed centers engaging said seats, and compression-springs holding said bar upon said centers, the axes .of compression of said springs being in the plane of said centers.

11. The combination with the stylus-bar, of a mounting therefor comprising a rock-bar to which said stylus-bar is rigidly attached, said rock-bar having conical seats, pointed centers engaging said seats, the taper of said centers being more acute than that of the seats, and coiled springs pressingsaid bar upon said centers, the axes of said springs being in the plane of oscillation of said bar.

12. The combination with the stylus-bar,

of amounting therefor comprising a rock-bar, pointed centers upon which said bar is seated, and coiled springs holding said bar against said centers, the points of the centers and the bearings of the springs against the bar being in the same plane.

13. The combination of the diaphragm, th stylus-bar carrying a stylus, centers upon which said bar is mounted to rock, and springs pressing said bar against said centers and acting in the plane of oscillation, said centers being in a line which intersects the axis of the stylus.

In testimony whereof I have signed this specification-in the presence of two subscribing Witnesses.

THOMAS H. MACDONALD.

Witnesses:

.A. B. KEOUGH, M. A. Foeo. 

